Nickel electroplating electrolyte



United States Patent 3,502,550 NICKEL ELECTROPLATING ELEC'I'ROLYTE Frank Passal, Detroit, Mich., assignor to M & T Chemicals Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 1, 1965, Ser. No. 506,005 Int. Cl. C23b 5/ 08, 5/46 US. Cl. 204-49 1 Claim ABSTRACT OF THE DISCLOSURE A process is provided for electroplating a semi-bright nickel deposit with a plating solution which includes therein as semi-bright additive piperonal and a watersoluble acetylenic compound. Also, a nickel plating solution is provided for said process which consists essentially of an acidic aqueous nickel plating solution and including as semi-bright additive therein a composition consisting essentially of piperonal and a water-soluble acetylenic compound, and such compositions.

This invention relates to the electroplating of nickel. More particularly, it relates to the electroplating of a semi-bright nickel characterized by a uniformly finegrained structure over a wide current density range; excellent ductility; very low sulfur content; low tensile stress; freedom from tendency toward dendritic growths (treeing) on high current density edges and corners. Semi-bright nickel obtained in accordance with this invention may also be easy to polish and buff to a high luster, if desired, with removal of a minimum of metal and with good flow characteristics permitting filling in of defects in basis metal.

As is known to those skilled-in-the-art one of the uses of semi-bright nickel is to act as an underlying layer for bright nickel. For this application the semi-bright layer may preferably contain an appreciably lower sulfur content than the bright nickel coating. The lower sulfur content permits the bright nickel layer to become anodic to the semi-bright layer in corrosive media thereby increasing lateral corrosion and slowing down the rate of vertical penetration or corrosion down to the basis metal. In such a duplex system when corrosion proceeds down to the semi-bright layer the vertical penetration may be slowed and any attack may proceed laterally along the interface of the semi-bright and bright nickel layers thus in effect protecting the basis metal. When the basis metal is relatively free of gross imperfections it may be plated with semi-bright nickel and bright nickel in thickness ratio of about 1:1 to 3:1 respectively and then usually followed by chromium plating. Since the higher thickness ratios are more common it is preferable that the semibright layer be fine-grained and uniform over a wide current density range so that the thinner bright nickel deposit can build up to its maximum luster over all significant areas. It is also preferable that the semi-bright nickel layer be so ductile and have such low tensile stress that spontaneous cracking in the high current density area down to the basis metal can be completely eliminated or minimized after bright nickeland chromium plating. This is particularly true since bright nickel may not be quite as ductile as semi-bright nickel and since the trend has been to use thicker chrominum deposits which are stressed and tend to promote cracking of underlying coatings if they are tensile stressed and not highly ductile.

Another use of semi-bright, ductile, low tensile stressed nickel deposits may be in electroforming. Here relatively thick layers of nickel are built up on a non-conductive matrix suitably conditioned by application of a prior conducting surface film of some metal such as copper or silver. The thick nickel layer may be then isolated from the matrix to give a rigid article which is the exact negative replica of the surface contour of the original matrix. For such an application it is important to have low tensile stress to avoid distortion on separation of the nickel from the matrix. It is also important because of the intricate and complex shape of some matrices that the nickel have the ability to give as uniform a thickness as possible, i.e. that the thickness ratio between high and low current density areas be as low as possible.

In duplex nickel plating the semi-bright layer has heretofore been deposited from various nickel plating bath formulations (Watts, sulfamate, Watts or sulfamate chloride-free etc.) which usually contain a plurality of cooperating additives (as grain refiners, stress relievers, anti-pitting agents etc.). Although it may be possible to produce a semi-bright nickel by prior art methods, numerous defects and short-comings have been encountered in commercial operation. Among these have been accumulation of decomposition products adversely affecting stress and ductility; non-uniform grain size in the operating current density range resulting in an undue demand on the bright nickel deposit to give maximum luster over all significant areas; formation of resinous or polymeric products which cause a number of surface defects; and poor solubility characteristics which make additive replenishment burdensome and inefiicient.

It is an object of this invention to provide a novel process for the electroplating of semi-bright nickel which give uniformly fine-grained deposits over a wide current density range; which can be. maintained ductile and lowtensile stressed over lengthy electrolysis times; which are relatively free of sulfur; which are free of any tendency toward high current density treeing; and which can be so receptive to bright nickel plating that maximum deposit brilliance can be achieved within ordinarily specified thicknesses of bright nickel. Another object of this in vention is to take advantage of the excellent physical properties of the deposits so as to permit their use in electroforming applications for nickel, particularly since the excellent throwing power permits the attaining of a uniformity of thickness distribution which has been found far superior to the prior art processes. Other objects will be apparent to those skilled-in-the-art on inspection of the following description.

In accordance with certain of its aspects, the novel process of this invention for electroplating a semi-bright, nickel plate onto a basis metal may comprise passing current from an anode to a metal cathode through an aqueous acidic nickel plating solution containing nickel compound providing nickel ions for electroplating of nickel, and including as semi-bright additive piperonal and a water-soluble acetylenic compound.

The basis metal onto which the semi-bright deposits of this process may be applied may include ferrous metals such as steel; copper, including its alloys such as brass, bronze, etc.; zinc, particularly in the form of die castings which may bear a plate of copper; thin metal coatings, e.g. of silver or copper on a non-conductive article which coating may be applied by reductive techniques; etc.

The novel baths of this invention may typically include Watts-type baths, sulfamate-type baths, mixed Watts-sulfamate-type baths, fiuoborate-type baths, chloride-free sulfate baths, chloride-free sulfamate baths, chloride-free mixed sulfate-sulfamate baths, etc.

A typical Watts bath which may be usm in practice of this invention may include the following components in aqueous solution, all values being in grams per liter (g./l.) except for the pH which is electrometric:

TABLE I Component Minimum Maximum Preferred Nickel sulfate heptahydrato 200 500 300 Nickel chloride hexahydrate 7 80 45 Boric acid 35 55 45 pH 3 4 A typical sulfamate-type bath which may be used in practice of this invention may include the following components:

TABLE II Component Minimum Maximum Preferred Nickel sulfamate 330 600 375 Nickel chloride hexahydrate i5 60 45 Boric acid 35 55 45 pH 3 5 4 A typical mixed Watts-sulfamate-type bath which may be used in the practice of the invention may include the following components:

A typical fiuoborate-type bath which may be used in the practice of the invention may include the following components:

TAB LE IV Component Minimum Maximum Preferred Nickel iluobol'ate 250 400 300 Nickel chloride hexahydra 45 60 60 Boric acid 30 pH 2 4 3 A typical chloride-free sulfate bath which may be used in the practice of the invention may include the following components:

TABLE V Component Minimum Maximum Preferred Nickel sulfate heptahydrate 300 500 400 Boric acid 35 55 45 pH 3 5 4 A typical chloride-free sulfamate bath which may be used in the practice of the invention may include the following components:

TA B LE V I Component Minimum Maximum Preferred Nickel suliamate 300 400 350 Boric acidt 35 55 45 pH 3 5 4 A typical chloride-free mixed sulfate-sulfamate bath which may be used in the practice of the invention may include the following components:

TABLE VII Component Minimum Maximum Preferred Nickel sulfate heptahydrate 100 250 150 Nickel sulfamate 165 300 194 Boric aeid 35 55 45 pH 3 5 4 It will be apparent that the above baths may contain compounds in amounts falling outside the preferred minimum and maximum set forth, but most satisfactory and economical operation may normally be effected when the compounds are present in the baths in the amounts indicated.

In accordance with practice of the process of this invention, there may be present in the nickel plating bath as semi-bright additive, (a) piperonal and (b) a watersoluble acetylenic compound. This additive composition may cooperate with or be compatible with the nickel plating bath.

Piperonal, also known as heliotropine, may be characterized by the following formula:

(IDHO R l 0 l wherein R may be hydrogen or an inert or non-reactive substituent. The piperonal additive may be used in this invention as piperonal se, or with the piperonal ring bearing inert or non-reactive substituents in any of the 2, 5, or 6 position. Typical inert or non-reactive substituents include alkyl, aryl, cycloalkyl, aralkyl, alkaryl, al kenyl, ether, halogen, ester, etc. Typical specific substituents may be methyl ethyl, propyl, phenyl, cyclopentyl, cyclohexyl, benzyl, tolyl, vinyl, propenyl, ethoxy, chloro, bromo, carboethoxy, etc. The preferred piperonal additive may be piperonal se. The piperonal additive may be particularly useful in refining grain size promoting ductility, and reducing tensile stress.

Excellent semi-bright electrodeposits may be obtained when the piperonal additive is used in combination with a water-soluble acetylenic additive. The water-soluble acetylenic compound may be particularly useful in enhancing uniformity and promoting leveling of the semibright nickel deposit.

Water-soluble acetylenic compounds which may be employed in this invention may be particularly characterized by a highly nucleophilic triple bond which is free from steric hindrance and thus has a clear and unimpeded path in approaching the cathode.

The preferred water-soluble acetylenic compounds which may be employed in the process of this invention to produce semi-bright nickel deposits may include asubstituted acetylenic compounds having the formula R2 R2CEC( lR it.

in which each of R and R may be substituents selected from the group consisting of hydrogen, alkyl, alkenyl,

alkynyl, hydroxy-substituted and alkoxy-substituted alkyl, alkenyl, and alkynyl groups, and R and R may together be a carbonyl oxygen; R may be a substituent of the group consisting of hydrogen, halogen, alkyl, alkenyl, alkynyl, hydroxy-substituted and alkoxy-substituted alkenyl and alkynyl groups, and substituted-alkyl groups having the formula incl di g hy yand alkoxyand alkyl-substituied aryl;

each of R and R may be substituents selected from the group consisting of hydroxy, alkoxy, carboxy-substituted alkoxy, formoxy, alkanoxy, halogen and polyoxy groups and R may also be an amino group including alkyl and aryl substituted amino group when R and R together form a carbonyl oxygen and R is an aryl group. Where R is a substituted-alkyl group having the above-illustrated formula, the acetylenic compound may be termed an a,e'-disubstituted acetylenic compound, since both carbon atoms vicinal to the same acetylenic bond contain either the same or a different functional group.

The compounds listed in Table VIII are illustrative of tX-SllbStItuted acetylenic compounds which may be used in plating baths in practice of this invention.

The novel semi-bright compositions or additives of this invention may preferably be used in nickel plating baths maintained at an acid electrometric pH, such as those of Tables IVII, typically the bath of Table I, in amounts of at least 0.02 g./l. of plating bath, preferably 0.02-1.2 g./l. Lower concentrations may give appreciable grain refinement but the deposits may be less glossy. The most preferred concentration may be from 0.05-1 g./l. of additive in the plating bath; Typically there may be present combined additive in the amount at least 0.02 g./l. of plating bath, which additive includes 0.01-1 g./l. of piperonal (including piperonal se and inertly substituted derivative thereof) and 0.010.2 g./l. of water-soluble acetylenic compound. When preferred acetylenic com- TABLE VIII.a-SUBSTITUTED ACETYLENIC COMPOUNDS 1' 2 R 3- CE C- (|3 1 Compound R R2 a R01 2-butyne-l ,4-diol H C2OH -O H 1,4-di-(Bhydroxyethyoxy)-2-butyne -H -CHO CHaCH OH -O CHzCH OH 1,4-diacetoxy-2-butyne H -CH O fiCHa 0 (If CH3 3-butyne-1,2diol --CH OH H H H 8-methyl-1-butyne-3-0L CH3 C H: -H -0 H 3methyl-1-pentyn-3-ol -C H CH H -O H 2-propyn-1-ol -H OH 2,5-dimethyl-1-octen 3-yn-5-ol C;H1 I CHa -(I3 Ha OH --C -CH;

3-methyl-1-nonyn-3-ol CflH13 -CH3 H -OH 2,4-hexadiyne-1,6diol -H H ---C E CH OH --OH l-methoXy-Z-propyne H H H 0 CH3 3-methoxy-3-methyl-4,6heptadiyne 'C2H5 CH; C E CH 0 CH3 3-ethoary-3,5,7-trirnethyl-1-octyne -CH; H O C2H5 l-formoxy-Z-propyne H H -O EIJH l-aeetoxy-Z-propyne -H H H -0 (5 CH3 3-methyl-1-n0nyn3-yl acetate C H13 -CH3 H -0 (Ill 0 Ha Phenyl-proplolamide /=O =0 CaH5 NH2 Phenyl-propiol-N-phenylamide V =0 V =0 CaHs N (OaH5) H Phenyl-propiol-N,N-dimethylamide V =O -CaH5 N (CH3) 2 3-methyl-1-butyn 3-yl acetate OH3 C'Ha H 0 (ll) CH:

O 1-chloro-6-methoxy-2,4-hexadiyne H C E C-CH2O CH; C1 3-chloro-3-m ethyl-4-hexyne C2H5 CH3 CH3 -01 l-bromo-Z-propyne H H -H Br 1,2-di-(fl-hydroxyethoxy)-3 butyne -C Hr-O-CHz -H -H -O CHzCHzOH 3-(B-hydroXy-y-chloropropoxy)-3- CzH5 CH3 -H CHzCl methyl-tpentyne. I

, O CHzCH O H 3-(fl- -epoxyprop oxy) -3-methyl-4- C2H OH:

pentyne.

Those acetylenic compounds which may be prepared in the instant invention include those containing at least one hydroxy moiety, and most preferably those which contain two hydroxy moieties, e.g. the beta-hydroxyethyl ether of 2-butyne-l,4-diol, i.e. l-(beta-hydroxyethoxy)-4-hydroxy-2-butyne, and the bis (beta-hydroxy ethyl ether) of 2-butyne-l,4-diol i.e. 1,4-bis (beta-hydroXy-ethoxy) -2-butyne.

Acetylenic compounds which may be employed in the instant invention also include the above compounds modified to include other substituents such as sulfonate groups or sulfate groups. Typical of such acetylenic compounds are the monoand di-sulfated products which may he formed by reaction of the beta-hydroxy-ethyl ether of 2-butyne-1,4-diol and sulfamic acid or of the bis-(beta-hydroxy-ethyl ether) of 2-butyne-l,4-diol and sulfamic acid.

pound containing hydroxy moieties, e.g. the beta-hydroxyethyl-ether of 2-butyne-1,4-diol and the his (be'ta-hydroxyethyl-ether) of 2-butyne-l,4-diol, are employed, the addi' tive may typically include 0.01-1 g./l., say 0.0l-0.l g./l., of piperonal and 0.01-0.1 g./l., say 0.01-0.05 g./l., of the acetylenic compound. The electrometric pH may typically be 25, preferably 3-4.

A preferred nickel plating solution may be a mixed Watts-sulfamate bath maintained at an electrometric pH of 4.0 containing g./l. of nickel sulfate heptahydrate, g./l. of nickel sulfamate, 45 g./l. of nickel cloride hexahydrate, 45 g./l. of boric acid, 0.05 g./l. of piperonal and 0.05 g./l. of the bis-(beta-hydroxy-ethyl ether) of 2-butyne-1,4-diol.

The additive components may be added to nickel plating baths as individual components or may be dissolved in separate solutions, e.g. 20-50 g./l., say 30 g./l. of

piperonal in an organic solvent such as isopropanol, etc., and -50 g./l., say g./l. of acetylenic compound in a solvent such as isopropanol, water, etc. When the acetylenic compound, typically the beta-hydroxy-ethyl ether of 2-butyne-1,4-diol or the bis (beta-hydroxy-ethyl ether) of 2-butyne-1,4-diol, is dissolved in water, there may be present a water-soluble nickel compound, preferably nickel sulfate heptahydrate, in mold-inhibiting amount typically 25-50 g./l., say g./l., thereby inhibiting mold formation in the solution containing the acetylenic additive. Other nickel compounds which may be employed in solution with the acetylenic compound as mold inhibiting components may include nickel chloride hexahydrate and nickel sulfamate. This solution may be added to the nickel plating solution in addition to any nickel compound already present therein.

Semi-bright nickel plating in accordance with this invention may be carried out by immersing a basis metal cathode into a nickel plating bath as hereinbefore disclosed. The anode may be either a soluble anode, typically nickel metal, or an insoluble anode, typically lead. If nickel is used as the anode, it is preferably SD type of nickel. Plating may be carried out typically in chloridecontaining baths for 10-60 minutes, say 30 minutes, at -60 C., say C., with mechanical or air agitation. The cathode current density may typically be 2.5-5 amperes per square decimeter (a.s.d.), preferably 5 a.s.d.

In accordance with certain aspects of this invention medium or very high-speed electroplating of semi-bright nickel may also be effected by a process comprising passing direct current from a substantially non-polarizing anode to a metal cathode through an aqueous nickel plating solution including at least one nickel compound capable of providing nickel ions for electroplating nickel, and including as semi-bright additive piperonal and a water-soluble acetylenic compound; maintaining the cathode current density during said plating at a level of at least 10 a.s.d., and maintaining a high relative velocity between said nickel plating solution and said metal cathode thereby obtaining a semi-bright, rapidly deposited nickel deposit.

The substantially non-polarizing anodes which may be used in the very high or medium speed electroplating aspect of this invention may preferably be insoluble anodes, such as lead which have very little tendency to polarize, even at very high current density, or certain soluble anodes, such as the commercially available SD type of nickel which has less tendency to polarize than other soluble nickel anodes and may be used at current densities as high as 40 a.s.d. The SD type of nickel is an electrolytic nickel containing a controlled amount of sulfur as nickel sulfide. When an insoluble anode is used the bath typically should be chloride-free. Such a bath may be replenished in nickel metal content and have its pH adjusted by the addition, of an alkaline oxide, hydroxide or carbonate of nickel, preferably in a separate regenerating tank.

Thus according to this high speed plating aspect of the invention a current density of over about 10 a.s.d., and preferably of 20-60 a.s.d., may be used, although a current even higher than 120 a.s.d. may be applied during electroplating of nickel using baths containing the novel additives of the invention. Plating carried out in this manner may permit deposition of predetermined thickness of semi-bright nickel in a time which is as little as 10% or less of the time required when ordinarily used plating conditions with soluble nickel anodes are used. Typically production of a semi-bright nickel plate 25 microns thick according to this aspect of the invention may require 3 minutes in contrast to 30 minutes for usual plating conditions.

When medium or very high speed electroplating is desired, a high relative velocity may be maintained be tween the bath and the cathode to replenish the cathode film with nickel ions as they are plated out therefrom.

Typically the high relative velocity between the bath and the cathode is maintained at a level equivalent to 60-320, say cm./ second. The agitation may be produced by vibration (including ultrasonic), rotation of the cathode relative to the solution, by pumping the electrolyte through the system and over the cathode surface or by very vigorous and directional agitation of the electrolyte with appropriately positioned propellers or other devices, etc.

The novel process of this invention may permit attainment of a 12.5 to 50 microns, say 25 microns, semibright nickel plate characterized by its fine grain, high ductility, hi h gloss, uniform appearance, and high covering power. The plate may also be characterized by its essentially sulfur-free character.

The plating baths may also contain optional additional constituents such as anionic wetting agents to reduce any tendency toward hydrogen pitting. High foaming anionic wetting agents such as sodium lauryl sulfate may be used in conjunction with mechanical agitation; and low foaming anionic Wetting agents such as sodium dialkyl sulfosuccinates may be used with air agitation. Although these wetting agents may commonly contain sulfur, unexpectedly, no increase in the sulfur content of the deposits may be observed when they are used with the additives of this invention. The wetting agents may typically be present in amounts of 0.1-1 g./l. of plating solutlon.

It is a further feature of this invention that the novel semi-bright nickel additive composition may be used in combination with other semi-bright additives in order to augment and extend advantageous features imparted by such other additives. Typical examples of such other additives which may have their characteristics extended are chloral hydrate, coumarin and coumarin derivatives such as oxyomegasulfohydrocarbon-di-yl coumarins, e.g. potassium 7-oxyomegasulfopropyl coumarin. Thus, semi-bright nickel plate obtained from a sulfamate plating bath having an electrometric pH of 4.0 containing 375 g./l. nickel sulfamate, 45 g./l. nickel chloride, 45 g./l. boric acid and 0.8 g./l. of potassium 7-oxyomegasulfopropyl coumarin, in 10 minutes at 6 a.s.d. and 60 C., may be characterized as highly leveled, very fine grained, of low tensile stress, and very ductile. These characteristics may be increased even more if 1 ml./l. of a 1:1 isopropanol water solution of 15 g./l. of the his (beta-hydroxy-ethyl ether) of 2- butyne-1,4-diol and 0.25 g./ l. of piperonal are added to the sulfamate plating bath.

Oxyomegasulfohydrocarbon-di-yl coumarins such as are disclosed supra may be prepared by reacting in a solvent dispersion eg of methanol, a hydroxy coumarin, a compound of the formula MOH wherein M is a metal, and a hydrocarbon sultone or by reacting a hydroxy coumarin with a salt of a hydroxy hydrocarbon-di-yl sulfonate such as sodium isethionate.

The following illustrative examples disclose nickel plating baths containing the novel additive of this invention, and electroplating processes wherein these baths are used.

EXAMPLE 1 1 liter of the following Watts-sulfamate bath may be prepared:

Nickel sulfate heptahydrate-ISO g./l. Nickel sulfamateg. l.

Nickel chloride hexahydrate--45 g./l. Boric acid-45 g./l.

pl-I electrometric-4.0

Water to 1 liter.

9 through the bath at 60 C. for 30 minutes to obtain a dull, grainy, non-uniform deposit.

In practice of the invention, 0.05 gram of piperonal and 0.05 gram of the bis (beta-hydroxy-ethyl ether) of 2-butyne-l,4-diol may then be mixed into the bath and the plating test repeated. This time, a beautifully fine grained, very ductile deposit of high gloss and very uniform appearance may be obtained. This deposit may also be characterized as being substantially free of tensile stress and as being substantially free of sulfur (i.e. as containing less than 0.003% by weight of sulfur).

EXAMPLE 2 1 liter of the following Watts bath may be prepared:

Nickel sulfate heptahydrate300 g./ l. Nickel chloride hexahydrate45 g./l. Boric acid-45 g./l.

pH electrometric3.8

Water to 1 liter.

The bath may be thermostatically controlled at 55 C. and air agitated, 0.05 gram of piperonal and 0.05 gram of the beta-hydroxy-ethyl ether of 2-butyne-1,4-diol may be mixed into the bath and electroplating carried out at a current of 5 amperes and at 55 C. for 30 minutes using a bagged SD nickel anode and a highly polished brass cathode strip pleated in 45 angles. The deposit obtained may be noted as being finely grained, very ductile, of high gloss, of very uniform appearance, desirably low in tensile stress and substantially free of sulfur.

EXAMPLE 3 1 liter of the following sulfamate bath may be prepared:

Nickel sulfamate375 g. /l.

Nickel chloride hexahydrate45 g./l. Boric acid-45 g./l.

pH electrometric4.0

Water to 1 liter.

The bath may be thermostatically controlled at 55 C. 0.2 gran1 of potassium 7-0xyomegasulfo-propyl coumarin may be mixed in the bath and electroplating carried out at a current of 5 amperes, at 5 C. for 30 minutes using a bagged SD nickel anode and a highly polished brass cathode strip pleated in 45 angles. The deposit obtained may be very fine grained, well leveled, very ductile, and lustrous with only a slight haze.

The above experiment may be repeated with the further addition to the bath of 1 ml. of a 1:1 isopropanol solution containing 30 g./l. solution of his (beta-hydroxyethyl) ether of 2-butyne-1,4-diol and 50 g./l. of piperonal. The characteristics of the deposit obtained are augmented and extended beyond the characteristics of the deposit produced in the first part of the example. Thus the later produced deposit may be noted as being even more fine grained, more ductile, still well leveled, and glossy and having low tensile stress.

EXAMPLE 4 1 liter of the following Watts-bath may be prepared:

Nickel sulfate heptahydrate-375 g./l. Nickel chloride hexahydrate-7.5 g./l. Boric acid45 g./l.

pH electrometric4.0.

Water to 1 liter.

The bath may be thermostatically controlled at 54 C. and mechanically agitated with propellers. 0.05 gram of piperonal, 0.2 gram of phenyl propiolamide, 0.2 gram of the disulfated reaction product of the bis (B-hydroxyethyl ether) of 2-butyne-l,4-diol and sulfamic acid and 0.5 g./l. of sodium lauryl sulfate wetting agent may be mixed into the bath and electroplating carried out at a current of 2.5 amperes at 54 C. for 30 minutes using a bagged SD nickel anode and a copper plated die cast handle having a surface area of about sq. cm. which may be scribed with a single pass of a 1.2 cm. wide zerogrit emery paper. Within 15 minutes a semi-bright deposit may -be obtained of remarkably high luster and fine grain size having scratched band virtually completely filled in.

EXAMPLE 5 1 liter of the following Watts bath may be prepared:

Nickel sulfate heptahydrate-300 g./ l. Nickel chloride hexahydrate45 g./l. Boric acid-45 g./l.

pH electrometric--4.0

Water to lliter.

The bath may be thermostatically controlled at 66 C. and mechanically agitated with propellers. 0.5 gram of a high foaming wetting agent, sodium lauryl sulfate, may be added to the bath. 0.1 gram of phenyl propiolamide may then be mixed in the bath and electroplating carried out at a current of 5 a.s.d. at 60 C. for 30 minutes using a bagged SD nickel anode and a highly polished brass cathode strip pleated in 45 angles. The deposit obtained may be a good, fairly fine-grained semi-bright deposit, but not quite adequate in grain size to permit building up luster rapidly upon bright nickel plating.

Theabove experiment may be repeated with the further addition to the bath of 0.5 g./l. of piperonal. The deposit obtained is much improved and may be characterized as being more fine grained, level, ductile, uniform in appearance, substantially free of tensile stress, substantially free of sulfur. Further the deposit may permit rapid build-up of luster upon bright nickel plating.

Although this invention has been illustrated by reference to specific examples, numerous changes and modifications thereof which clearly fall within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. A nickel plating solution consisting essentially of an acidic aqueous nickel plating solution including a nickel compound capable of providing nickel ions for electrodeposition of nickel on a basis metal cathode and including as semi-bright additive 0.011 g./l. of said plating solution piperonal and 0.010.2 g./l. of said plating solution of a water-soluble acetylenic compound selected from the group consisting of the bisQS-hydroxy-ethyl ether) of 2-butyne-1,4-diol and the fi-hydroxy-ethyl ether of 2-butyne-1,4-dio1.

References Cited UNITED STATES PATENTS 1,564,414 12/1925 Hoff 204-50 2,795,540 6/1957 Brown 204--49 2,800,440 7/1957 Brown 204-49 2,800,441 7/ 1957 Brown et al. 204-49 2,900,707 8/ 1959 Brown 204-49 XR 3,002,902 10/ 1961 Foulke et al. 204-49 3,002,904 10/1961 Foulke et al. 20449 3,108,933 10/1963 Johnson 20451 3,140,988 7/ 1964 Clauss et a1. 204-49 3,367,854 2/ 1968 Passal 204-49 FOREIGN PATENTS 871,276 6/1961 Great Britain.

OTHER REFERENCES Wesley, W. A., et al., Electrodeposition of Nickel at High Current Density," reprint from the 36th Annual Proceedings of the American Electroplaters Society, pp. 3-15, 1949.

HOWARD 1S. WILLIAMS, Primary Examiner G. L. KAPLAN, Assistant Examiner 

